It is frequently necessary to inject lubricating oils, corrosion inhibitors, and other chemicals into the flow lines and equipment at oil and gas wells and other petroleum facilities. Existing injection systems typically include a pump for injecting a chemical into a system, and some timer, metering valve, or other controller to activate the pump at predetermined intervals. (As used in this application, “chemical” refers to any chemical fluid, including lubricating oils). Because it is important to know the total volume of chemical injected into a fluid system over the period of operation, more sophisticated systems include verification devices to determine the quantity of chemical injected.
Examples include positive-displacement pumps for injecting chemicals into a pipeline, a controller, a flow switch connected to the outlet side of the pump, and an inlet meter for metering the chemical to the pump. The controller typically activates the pump for a predetermined number of strokes. From the number of strokes and a preset pump displacement setting, the purported volume of chemical injected can be calculated. In prior-art systems, the state of the pump is either assumed from the commands sent to it, or else the state is monitored by pressure switches that detect pressure in the line to be charged. The first method does not detect failures at all, and the second method is prone to error because merely moving a valve or pump element can cause spurious pressure changes within a pressurized system.
Such injection systems have advantages and improvements over the prior art techniques and devices, but they provide only coarse chemical usage data. While these systems do provide some quantitative raw data for analysis, adjustment and accountability of the chemical usage, they do not have any capability to present such data in a useful format to facilitate audit or reporting of system operation. The systems are also costly and have to be operated by experienced persons. It would be advantageous to have the injection system controlled centrally from some remote point by appropriately trained and informed persons.
Further complicating the problem is the number of flammable gases that may be present at oil and gas wells, such as mixtures of oxygen, methane, ethane, propane, hydrogen sulfide and others. Similar potentially dangerous environmental conditions exist in locations where petroleum products are being recovered, refined or processed. hazardous environmental conditions may also exist in industrial areas where large quantities of dust are present, such as in grain handling facilities or pulp and paper mil's. Standardized classifications for the various types of hazardous locations have been adopted and assigned by regulatory agencies according to the nature and type of hazard that is generally present or that may occasionally be present.
Because electrical components may generate heat and sparks sufficient to ignite a flammable gas or other flammable mixture under even normal operating conditions, such components must be carefully selected and installed when used in an area that is classified as hazardous. More specifically, the components must exceed certain minimum standards as to such characteristics as power consumption, operating temperature, current and voltage requirements, and energy storage capabilities. These standards are also established by regulatory authorities and vary depending upon the particular hazardous environment.
Certain electrical devices are intrinsically safe. An intrinsically safe device may be generally described as a device that during normal operation, as well as operation during any fault condition, cannot cause a spark or achieve a temperature sufficient to ignite the gas or other substance that is present. If a device is not intrinsically safe, other means must be provided to ensure that the device cannot serve as a source of ignition.
There is thus a need for a chemical injection system that can be centrally controlled, operate automatically, provide and report the accurate dispensing of chemical injections, and also be intrinsically safe in hazardous environments.